/*-
 * Copyright Rusty Russell IBM Corporation 2007.
 * Copyright 2019 NXP
 * This header is BSD licensed so anyone can use the definitions to implement
 * compatible drivers/servers.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of IBM nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL IBM OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * $FreeBSD$
 */

#ifndef VIRTIO_RING_H
#define VIRTIO_RING_H

/* 这标志着一个缓冲区继续通过下一个字段. */
#define VRING_DESC_F_NEXT           1U
/* 将缓冲区标记为只写(否则为只读). */
#define VRING_DESC_F_WRITE          2U
/* 这意味着缓冲区包含一个缓冲区描述符列表. */
#define VRING_DESC_F_INDIRECT       4U

/*
 * 主机使用used->flags标记来提醒客户端: 当添加缓冲区时, 不要打断.
 * 这是不可靠的, 所以这只是一个优化. 如果缓冲区不足, 客户端仍然会打断.
 */
#define VRING_USED_F_NO_NOTIFY      1U
/*
 * 客户端使用avail->flags标志来建议主机: 当消耗缓冲区时不要打断.
 * 这是不可靠的, 所以这只是一个优化.
 */
#define VRING_AVAIL_F_NO_INTERRUPT  1U

/* VirtIO环形缓冲区描述符: 16字节. 这些可以通过"next"链接在一起. */
struct vring_desc {
    /* 地址(客户端物理地址). */
    uint64_t addr;
    /* 长度. */
    uint32_t len;
    /* 如上所示的标志. */
    uint16_t flags;
    /* 通过next链接未使用的描述符. */
    uint16_t next;
};

struct vring_avail {
    uint16_t flags;
    uint16_t idx;
    uint16_t ring[1];
};

/* uint32_t在这里用于填充ID. */
struct vring_used_elem {
    /* 所使用的描述符链表的开始索引. */
    uint32_t id;
    /* 被写入的描述符链表的总长度. */
    uint32_t len;
};

struct vring_used {
    uint16_t flags;
    uint16_t idx;
    struct vring_used_elem ring[1];
};

struct vring {
    uint32_t num;
    struct vring_desc *desc;
    struct vring_avail *avail;
    struct vring_used *used;
};

/*
 * 环形缓冲区的标准布局是一个连续的内存块, 看起来像这样. 我们假设num是2的幂.
 *
 * struct vring {
 *      # 实际的缓冲区描述符(每个16字节)
 *      struct vring_desc desc[num];
 *
 *      # 环形缓冲区未使用的描述符头.
 *      __u16 avail_flags;
 *      __u16 avail_idx;
 *      __u16 available[num];
 *      __u16 used_event_idx;
 *
 *      # 填充到下一个对齐边界.
 *      char pad[];
 *
 *      # 环形缓冲区已使用的描述符头.
 *      __u16 used_flags;
 *      __u16 used_idx;
 *      struct vring_used_elem used[num];
 *      __u16 avail_event_idx;
 * };
 *
 * 注意: 对于VirtIO PCI, 4096字节对齐.
 */

/* 将使用的事件索引发布在可用环形缓冲区的末尾, 反之亦然. 为了向后兼容, 它们位于末尾. */
#define vring_used_event(vr)  ((vr)->avail->ring[(vr)->num])
#define vring_avail_event(vr) ((vr)->used->ring[(vr)->num].id)

static inline int32_t vring_size(uint32_t num, uint32_t align)
{
    uint32_t size;

    size = num * sizeof(struct vring_desc);
    size += sizeof(struct vring_avail) + (num * sizeof(uint16_t)) + sizeof(uint16_t);
    size = (size + align - 1UL) & ~(align - 1UL);
    size += sizeof(struct vring_used) + (num * sizeof(struct vring_used_elem)) + sizeof(uint16_t);
    return ((int32_t)size);
}

static inline void vring_init(struct vring *vr, uint32_t num, uint8_t *p, uint32_t align)
{
    vr->num   = num;
    vr->desc  = (struct vring_desc *)(void *)p;
    vr->avail = (struct vring_avail *)(void *)(p + num * sizeof(struct vring_desc));
    vr->used  = (struct vring_used *)(((uint32_t)&vr->avail->ring[num] + align - 1UL) & ~(align - 1UL));
}

/*
 * 以下内容用于VIRTIO_RING_F_EVENT_IDX.
 * 假设给定的event_idx值来自另一个大小, 如果我们刚刚将所有从old增加到new_idx,
 * 我们是否应该触发一个事件?
 */
static inline int32_t vring_need_event(uint16_t event_idx,
                                       uint16_t new_idx, uint16_t old)
{
    /*
     * coco begin validated: 这个函数不需要测试, 因为它没有在rpmsg_lite实现中使用
     * (只从vq_ring_must_notify_host()的未使用部分调用).
     */
    if ((uint16_t)(new_idx - event_idx - 1U) < (uint16_t)(new_idx - old)) {
        return 1;
    } else {
        return 0;
    }
}

#endif /* VIRTIO_RING_H */
